1. Field of the Invention
The present invention relates to a simulator utilizing photogrammetry for use, as a mechanical aid, in surgery, for determining potential paths for the implantation of probes through the human body, particularly the brain.
2. Prior Art and Technical Consideration
For a large number of patients suffering from epilepsy, the disease cannot be controlled by medication and their only hope of cure is through surgery which rests in locating and destroying the epileptic area in the brain. Unfortunately, the present operational technique still deals with a non-negligible limitations and the possibility of curing most epileptic patients is yet quite a challenge.
The technique presently being applied is based mainly on an analysis of the behavior of electric waves, so called "depth waves", that occur within the brain during an epileptic stroke. For this purpose, probes of the type disclosed in U.S. Pat. No. 4,245,645 of Jan. 20, 1981 are used of which the tips, when the probes are implanted in the cerebral cortex, constitute a series of waves detectors capable of precisely localizing diseased areas of the brain. It is obvious however that the implantation has to be done with great skill, care and knowledge, to avoid the probes striking any brain vessels, particularly arteries, which would provoke hemorrhages. This is precisely a limitation, if there is, in the present technique which, otherwise, is extremely promising in the treatment of not only epileptic but also of other types of brain diseases. Stated otherwise, the neurosurgeon ought to be provided with a tool that would allow him to rapidly and easily determine with assurance, safe implantation paths through which probes can be driven without affecting any blood vessels.
Presently, the search for available probe implantation paths through the labyrinth of veins and arteries in the brain is carried out by means of angiographs of the patient's brain. Tomographs are also used to complete the image necessary to arrive at a diagnosis. Up to date, more them 1500 probes have been implanted and the method used has been found awkward because of the restraint resulting from the fact that the probes have to be introduced perpendicularly to the profile plane of the head. For medical reasons, neurosurgeons have, for a long while, wanted to get away from this restraint and have sought the possibility of reaching any zone of the brain by using all potentially available directions for implanting probes.
The solution proposed by the present invention is based on the application, to radiography, of a principle known as stereophotogrammetry. Stereophotogrammetry may be broadly defined as a science intended to obtain various measurements from their stereoscopic images of the object, that is from two images of that object taken from two different viewing directions. From the start, this science has been used chiefly in establishing maps from aerial photographies. However, its basic principles are just as well applicable to other types of images, such as radiographs.
From the middle of the present century, much has been written about photogrammetry in relation to radiography. Studies have recently shown that it is possible to locate, by modern photogrammetric methods, a radiographed point with an accuracy of the order of 0.1 mm. Based on this acquired knowledge, the simulator according to the present invention has been devised and it allows, as a preliminary important step, the determination on a stereoscopic view of the brain of potential paths that can be followed by probes to reach predetermined points in the brain without any danger of striking a vein or an artery.
The principle underlying the present invention is an extension of a concept well known in photogrammetry which is the "floating point", or floating mark. The term "floating" comes from the possibility to move a reference point anywhere within the whole space of the model of an object seen in stereoscopy. To achieve this movement, it is sufficient to move the reference point in relation to the stereoscopic image. In photogrammetric language, this means modifying the x-parallax of the reference point along with tis x and y movements to thus change its position in space in the stereoscopic model of the object.
Now, if it is possible to float one such reference point, it is surely possible to float two of them and if both points are joined, by using some artifice, then it becomes possible to create a "floating line".
By assimilating this floating line physically to a probe, it will be appreciated that the probe may be displaced through a three-dimensional view of a patient's brain, obtained by known stereoscopic methods. In this manner, it becomes possible to establish various potential paths, through the brain, which would be suitable for the implantation of a probe. By means of a technique, again derived from photogrammetry, the precise position of the path can be obtained by measuring the image positions.